How does the Willer bus pass work?

Hey, I was wondering how exactly does the Willer bus pass work? actually, more specifically, how does the purchase process work?

I understand that you have to buy it outside of Japan. Since I'm currently in Japan, I will ask my parents to buy it. However, how does the process work? Do you have to decide the exact route/time for all of your dates when you purchase? What form is the bus pass? Is it physical as in they send it to you via mail? Or is it electronic as in you print it out?

If all routes/times don't have to be decided when you buy it, how do you make the reservations? Online I guess... But can it be made inside Japan?

Thanks in advance!

It works as follows:

1) you create a user account with Willer
2) you purchase online by credit card

Then, your bus pass will be associated with your Willer user account. You get a confirmation by e-mail that you purchased the pass, but the actual pass is just a virtual association to your user account.

Afterwards, you can make seat reservations for your bus rides on the Willer website. All you have to do is to log into your Willer user account and use the designated bus pass reservation engine to make reservations.

In other words: it happens all online on the Willer website